DEVELOPMENT OF A WALL LIBRARY IN BIM S METHODOLOGY Luís Correia Nobre Araújo

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1 DEVELOPMENT OF A WALL LIBRARY IN BIM S METHODOLOGY Luís Correia Nobre Araújo Instituto Superior Técnico Technical University of Lisbon, Av. Rovisco Pais 1, Lisbon, Portugal ABSTRACT The construction of a building is an activity that involves multiple parties in a constant decision process which lead to a certain economic, social and environmental impact. Nowadays, the construction process resides mainly on a work environment based in computer aided design systems (CAD) and in a fragmented collaboration process between the different actors enrolled, promoting errors and making it difficult to decide. This limitations lead to inefficient communication, promoting construction errors and cost overruns. It s during the initial project phase that decisions have a greater impact on a building, so it s important that different designers are based on a precise data, in order foster their decisions throughout the project development. Presently, Building Information Modeling (BIM) methodology is presented as an alternative to achieve a better product. In this context, the study evaluates and compares the capabilities of BIM methodology with the work environment based on CAD software, aiming on how designers can obtain an agile, precise and updated information related to the construction solutions of exterior walls throughout the design, construction and management of the building life-cycle. The work involves the generation of a BIM parametric model, a single family house, and the creation of a parametrical library of objects related to constructive solutions of exterior walls with frequent application in the national market. The information centralized in the model, is used to obtain technical drawings and perspectives to support calculation and the budget of the project, environmental impact and building post-occupancy management. The main advantages and limitations of BIM methodology are identified when comparing alternative constructive solutions, and shows its ability to support decisions by stakeholders during the development of the project. Keywords: BIM, Exterior walls, Parametric modelling, Information extraction 1. INTRODUCTION The current working methods used by technicians from different areas involved in construction process are based on CAD, a technology that has been stalled. Although the methodology BIM exist for over 20 years, it only started to be considered by companies and governments during the last decade for reasons of competitiveness and a away to achieve efficiency. As an architect, with knowledge acquired from working in CAD environment and architecture design coordination, the importance of avoiding drawing errors, repetitive work and approach the different stakeholders, is essential to avoid conflicts and overrunning of costs. On the other hand, the need for fast and reliable information relating with different construction solutions is essential to designer, to be able to support his decisions. The choice of exterior walls in a construction has a considerable effect in the budget, in the environment and for society. So it s essential to provide a quick access to multiple information about different wall solutions 1

2 to the parties enrolled. Currently, the impact of the choice of a particular solution is normally obtained on an advanced stage and by using multiple and complex software, where only small things can be changed. Therefore, BIM methodology, is presented as an alternative to CAD work environment. It can be used to get information associated with the multiple stages of building construction process and lifecycle management and to assist all the parties to support their decisions. This study is intended to evaluate the modelling capabilities of Revit, a software that uses the BIM concept, to model a set of constructive solutions of exterior walls applied in a model and evaluate how they can provide information to the designer. For this purpose, the following objectives were established: Understand BIM s methodology, the origins and how is being applied, it s limitations and advantages; Identify different exterior wall solutions currently used in the national market; Resorting to a BIM software, Revit 2016, to model the architectural and structural components of a house analysing the steps performed and how it can be used to generate a library of exterior walls; Evaluate Revit potential and limitations to extract information related with the exterior walls. 2. BUILDING INFORMATION MODELLING (BIM) The construction of a building is a collaborative process involving different interests in the areas of Architecture, Engineering and Construction (AEC). Currently the construction of a building different parties due to the requirements of civil society such as architecture, structure, AVAC, security, sustainability, water fulfilment and drainage, among others (Kymmell, 2008). This growing demand requires a greater level of collaboration and coordination between the different actors enrolled and proper planning of resource management. Despite of the technological level of development achieved by the introduction of 3D CAD tools, the construction process still faces some conflicts resulting from the exchange of documents based on incoherent and wrong information, which can lead to wrongs decisions of all participants. Eastman et al (2011) points out that one reason for the low productivity inherent in the activity, arises from problems due to 2D drawing communication, the time required to obtain all the information related to the building, the cost estimation and to obtain technical drawings. As this information is usually obtained at the final stages, it is economically impracticable to change the plan to minimize the impact of initial decisions. It s in this context that BIM methodology was developed. Despite of BIM s concept exists since 70 s, Eastman et al (2011), describes BIM model of a building as a digital model that will be built during all phases of the project and allows multiple analysis and control of the building process. The BIM model must contain information, not only geometrical but also to support construction, fabrication, consulting and maintenance, and to provide more interconnected work processes and therefore promote final results of a higher quality and lower cost. Parametric modeling allowed by BIM methodology is the main difference allowing data mining to obtain quantities of materials and budgets, establishing constructive process, the simulation of environmental performance and energy building or assembly indication, 2

3 helping building maintenance an improving life cycle management (Garber, 2014). So BIM provide different uses (Figure 1) of information centered on the model, which is considered nd dimensions. The 3D model relating to spatial modeling; 4D model is added to the time variable; 5D model covers the project costs; 6D and 7D model introduces the maintenance and management of the building's life cycle and sustainability s analysis [W1]. BIM methodology is being assumed by the governments and AEC companies as way of work that must be gradually adopted. Different countries are trying to adopt BIM aiming the modernization of the construction industry, to achieve cost reduction and improve construction and life cycle management. Construction companies have been changing their working methods in order to be able to adopt the Figure 1 - different uses of BIM [W2] technology and achieve the objectives proposed by the government, aided by government assistance mechanisms. In Portugal despite of some public initiatives, the biggest effort comes from the biggest companies, to raise their competiveness in International markets and decrease the construction risks. The museum of art, architecture and technology of EDP is one of the buildings that the constructor SOMAGUE use BIM to improve better comprehension of project, to avoid conflicts between different disciplines and unexpected costs. (FUNDEC, 2015). Table 1 shows some of the benefits identified for different parties in process of construction. Table 1 - Benefits of BIM s methodology For owners and More participation and information during the project and construction (Eastman et al., 2011) managers of the decreasing the conflicts because the collaboration is more accurate and accessible (Smith building et al, 2009). More control of building s life-cycle management (Kymmell, 2008) and time spent in construction and during the design decreases leading to a better product (Kymmel, 2008; Eastman et al., 2011); Project elaboration Construction activity Provide earlier accurate information for initial decisions to achieve effective changes due to BIM s software analytical capacity (Eastman et al., 2011), provide an automatic creation of technical drawings (Kryghel, et al., 2008) and gathers all the building information in one file (Garber, 2014) The access to BIM model allow construction companies to participate as so the manufactures, leading to a more optimized construction process (Azhar, et al., 2008). Estimating costs are accurate and easy to obtain (W3) and construction management can be prepared earlier (Azhar, et al., 2008). Quantifying the economic, environmental and social impact of different construction and technical solutions to apply in a building, is a challenge for the designer (Wang et al., 2005). This paper discusses the importance of the exterior walls and its impact on construction. Along with the roof, forms the shell of the building, who is responsible for controlling the conditions of the indoor environment, such as 3

4 privacy, acoustic comfort, thermal comfort, structural safety, the aesthetic impact, among others. Thus the choice of an exterior wall has an important impact on environment, urban aesthetics and on budget. 3. EXTERIOR WALLS To model and extract all capabilities of BIM, it s necessary that the parametric object that is going to be modelled, has the correct information associated. As well, the designer should be able to quickly access to different options of exterior walls, so he could decide for different conditions the right wall to use. The paper considers the study of the main walls used in Portugal. Therefore, a research throughout the different types of walls has been made. Although we may find different systems, they must respond to environmental and people s demand, for instance, they should protect the users from outside, ensure stability and safety in case of fire, earthquakes and explosions. Also, they should ensure comfortable conditions adapted to the environment where they are built. The common facades used in Portugal, as we can see in table 2 are the made of earth (1), wood (3), concrete wall (6) or stone (2), prefabricated panels (8), wall fabricated with masonry brick (4) or concrete blocks (5), self-supporting walls such as Light Gauge Steel Frame (7). Also the walls of cork, plaster and cement are used although with less expression. Table 2 - Types of walls [W4]; 2- [W5]; 3- [W6]; 4- [W7]; 5- [W8]; 6- [W9];7- [W10]; 8- [W11]; The wall, as a building component should check a number of requirements. For its application must be known its main characteristics and physical properties. The use of an exterior wall, depends on the different materials and corresponding physical and mechanical properties. So to perform multiple analysis and support decisions, it s necessary to establish attributes that can be associated with parametric objects of exterior walls, to achieve an accurate database accessible to the different parties enrolled. Thus the parameters to be attached to BIM objects should consider studies such as thermal analysis and energy efficiency, construction planning, construction and maintenance costs, provide maintenance plans, among others. In this study where considered parameters related to the physical and mechanical properties, the sound transmission rate, the fire-rate requirements and also the relevant aspects for management, construction and maintenance, and the environmental impact. Thus, the chosen parameters joint with the respective solution are physical parameters such as: thickness (m), superficial mass(kg/m²), thermal resistance (m²k/w), thermal transmittance(w/m²k). Economic parameters like construction cost ( /m²), maintenance cost ( /m²), demolition cost( /m²) and man-hour 4

5 rate (man-hour/m²). The acoustic parameters, sound transmission rate due to aerial transmission (db), the fire rate parameter and environmental parameters such as embodied primary energy (EPE) (Kwh/m²). All these parameters are compiled in an information structure that must be added to each construction solution for exterior wall. The construction solutions to be modelled are (table 3): 2 solutions of double wall brickwork with a layer of air partially filled with a thermal insulator; External Thermal Insulation Composite System (ETIC), that consist of an outer insulator coated, fixed mechanically or by gluing in brick support panel (3); Ventilated facade insulated on the outside in a brick panel with ceramic tiles spaced from the insulator to allow wall ventilation (4); Light Gauge Steel Frame System, constituted from interior to exterior, 2 gypsum panels for interior, insulator panels made of rockwool, OSB panel, and for exterior an insulator panel cover with mortar (5). Table 3 - Exterior wall construction solutions with associated parameters Double wall brickwork ( ) cm Double wall brickwork ( ) cm Ventilated facade ETIC LGSF Type of exterior wall Physical parameters Thickness (m) 0,37 0,33 0,35 0,32 0,235 Superficial mass (kg/m²) Thermal resistance ((m²k)/w) Thermal transmittance ((m²k)/w) 300,84 277, ,77 86,25 3,08 2,95 1,73 2,11 5,43 0,307 0,32 0,525 0,44 0,179 Economical and management parameters Construction cost ( /m²) Maintenance cost ( /ano.m²) Demolition cost ( /m²) Man hour rate (man.hour/m²) Sound proof to aerial transmission (Db) 75,28 73,28 158,72 100,21 111,73 2,75 2,75 27,1 11,70 8,94 22,55 20,86 35,25 18,13 33,23 1,795 1, ,381 1,38 Sound parameters

6 Fire safety parameters Firerate A1 A1 F180 E180 F60 Environmental parameters EPE (Kwh/m²) 201,19 181,34 214,02 164,67 141,88 4. CREATING THE EXTERIOR WALL LIBRARY The methodology BIM requires the generation of a digital model. The architectural and structural model created for the selected case study is obtained with the Autodesk Revit 2016 software. The project to be modelled refers to a single-family housing located in Tavira, Portugal, with 2 upper floors, a basement, used as garage and storage and a rooftop. The structure consists of the traditional system of columns, beams and slabs of reinforced concrete. The modelling involved the development of the terrain, the structure, the architectural components, such as pavements, interior walls, doors, and windows and other architectural components such as handrails. The table 4 show the sequence of steps taken during the modelling of the BIM model. Table 4 - Modelling sequence Initial settings 1. Define the projects units 2. Setting the grid of main walls and pavement implementation 3. Setting of the levels Terrain 4. Adding the terrain level points Structural component 5. Creation of structural columns and beams Architectural Component 6. Creating basic walls (interior and exterior walls) 7. Creating floor 8. Creating windows and doors 9. Creating Stairs 10. Adding Components The method to model external walls was carefully explained and detailed. Since Revit Library, don t contain the main walls used in Portuguese construction it s necessary to create them. 5 types of walls were identified with different parameters, some of them don t exist in the default wall properties of Revit. During the modelling, the external walls of the house were obtained using the default walls of Revit. Although, to model the required walls, was necessary to understand how Revit conceives them. The walls are the junction of multiple materials that will assign the final properties of the wall. Therefore, to create it was necessary to identify materials, how they are created and their properties, to achieve an accurate wall. Revit contains some of the materials used such as concrete or mortar, although materials used, such as OSB panels or gypsum panels need to be created. Revit considers different properties with different purposes to define a material. The properties used by Revit depend on the material, but the main are the Identity: where is stored information such as description, comments, manufacturer, model mark, among others; graphical properties: where id defined it s colour, surface and cutting pattern; appearance properties: to obtain realistic perspectives introducing textures of material; physical properties: mechanical properties like its behaviour, young s modulus, poison s ratio, shear modulus and density, thermal expansion coefficient. With all materials created we can model any type of wall 6

7 composed in multiple layers. Although there are some parameters relevant for the study of BIM abilities that don t appear in the default settings such as the costs of construction, costs of maintenance and demolition, superficial mass, the maintenance plan, among others, so, as observed in Figure 2 this parameters were added to the parametric model of the exterior wall. With the exterior wall library created, the parametric objects were implemented in the BIM s model. Figure 2 Parametric object of ETIC Wall with multiple parameters added 5. EXTERIOR WALL LIBRARY APPLICATION Using the library of constructive solutions of exterior walls modelled, the study of Revit abilities to provide information to the designer is essential to understand the possibilities of BIM s methodology when comparing with CAD work environment. Therefore, different dimensions were analysed such as the capability of the model to provide information and obtain documentation related to the building, the production of technical drawings, budgeting and how can be obtained maps with quantities of material, construction planning activities, maintenance and building management, and how is performed environmental sustainability analysis. Modelling alternative solutions: To alternate exterior walls it s a simple process, almost automatic although when the replacement is made, all the structure need to adapt to that solution. Since we have different thickness of the exterior wall, the model should adapt to a new solution which means that can occur changes in interior areas, also the joints between interior wall and exterior walls can change place. As we can see in figure 3, the interior wall stayed in same place leading to a modelling error. So these kind of errors need to be manually corrected and joint conditions carefully defined; Figure 3 - Exterior/interior wall joint Drawing production: The graphical documentation associated with a project consists of plans, sections, elevations and construction details. As the 3D digital model is parametric, it contains all the information associated with the composition of each design element so Revit can create any kind of drawing. Nevertheless those drawings must be completed with information such as dimensions, object 7

8 identifiers, room identifiers, all the information that user wants. Moreover there are specific points of the model that must be carefully examined since they can lead to errors and wrong information. For instance the joint between a column and the wall. As we can see in figure 4 there are two errors, the wall overlapping the column, which need to be manually corrected and, the insulation that was interrupted by the column, leading to a wrong detail. This last error can be avoided by modelling this parts or providing a detail for this kind of situation. Besides that and the additional work to correct some errors and complete the drawing, the generation of a drawing it s quicker when comparing with CAD environment. Figure 5 illustrate a drawing with different kind of information. Figure 4 Material overlap Figure 5 Multiple information in a drawing 4D model: Is the combination of the elements of BIM 3D model with time. Although Revit allow to attach to each object parametric 3D model information on the planning of the work, such as labor productivity has few features comparing with other software. Although Revit allow to create tables with estimated times of construction of each wall because it s know the man-hour rate for each solution; 5D model: The 3D model allows to obtain the amount of materials used in construction. As the model objects are parametric, the composition the wall material is known, as well as, the area or volume of each element, so it s easy to obtain quantities of material. Also if the parametric object is associated with the cost we can extract quickly a table with wall costs estimation (Table 5); Table 5 - Costs estimation for double brickwork wall (11+11cm) 6D and 7D model: This dimensions are related with lifecycle-management and sustainability analysis. Buildings are responsible for 40% of energy consumption all over the world, thus the interest to know how the building is going to behave it s an information that must be quick access to the designer Revit has features (Green Building Studio) that allow sustainability analysis to be used in different phases of the project. In spite of using an algorithm used in software such as equest, the analysis doesn t 8

9 considerer Portuguese regulations, so it must be carefully used as a tool to help decide between solutions. For management building lifecycle it is associated with each parametric object of exterior wall solution, a set of information that can be extracted by Revit or implemented in software suitable for construction management. Revit allow to obtained lists that refer to the maintenance aspects for each type of exterior wall, as well as other information useful for maintenance activities. 6. CONCLUSIONS This work require learning one of the BIM s software, as well understand the methodology, providing personal and technological enrichment. This study gathers the basic theoretical and practical knowledge in order to be able to establish a critical view of BIM concept. Despite the BIM concept exists for some decades, the application of the methodology is still new, with a strong increment in the AEC during the last decade. It covers different phases of the construction process, design, construction and building management, centralizing the process into a single digital model accessible by all participants. It promotes communication among experts reducing the costs increasing the productivity of the process and gathering all the participants. To model a parametric object of exterior walls, the research related to the characterization of different type of exterior walls led to the analysis of different types of exterior walls in the national context, and the most important solutions were identified. Also in order to establish a library of parametric objects of exterior walls were considered and studied multiple parameters, however, other parameters from different disciplines could be added. Revit software was used to model the parametric objects of exterior walls in single-family house. The modelling process differs from CAD system because Revit uses objects with associated information, like its material composition, the boundary conditions, costs, maintenance plans. For each type of wall were easily introduced parameters considered relevant to the characterization and for decision making. The library created is a digital database, and can be improved with introduction of new information. Throughout Revit software some analysis were performed. Revit can be used to perform different tasks, being assured the reliability of information in terms of design, consistency and keeping it updated. Production of technical drawings in particular plans, sections, elevations, construction details and perspectives of the 3D model is automatic and the information is always updated. However, it was necessary some adjustments in the model and drawings when changing between different solutions. Revit has limited capacities in other dimensions such as 4D model, although it allows the creation of basic tables. That can be overlap by migrating to other software such as Navisworks, with more 4D features. Obtaining material quantities and budget estimation are carried out automatically, but the elements not included in the digital model weren t considered. For maintenance purposes Revit allow to set of information of procedures of each component and add maintenance periods for equipment and materials. Also the sustainability analysis provided can be used to inform the designer about different solutions. BIM is a methodology that is not free of errors, many of the limitations analysed came from the fact that it is still a recent methodology. Software, plug-ins and libraries are still growing, and companies, manufacturers, and designers are adapting to this methodology, investing in learning and change 9

10 working methods. The present study and the development of and exterior walls library adjusted to the national market is one of the essential parts of a parametric object database for the construction process, that can help the designer to support his project decisions, increasing the efficiency of his work and the quality of final product. 7. REFERENCES AZHAR, S., HEIN, M., Sketo, B. (2008), - Building information modelling (BIM): Benefits, risks and challenges - Proceedings of the 44th ASC National Conference USA CIFE ( 2007). CIFE Technical Reports - EASTMAN, C., TEICHOLZ, P., SACKS, R., LISTON, K. (2011) BIM Handbook A guide to Building Information Modeling for owners, Mangers, Designers, Engineers, and Contractors - John Wiley & Sons, inc, New Jersey, USA FUNDEC. (2015) A tecnologia BIM no desenvolvimento de projectos.18 October 2015 IST - Lisboa GARBER, R. (2014) BIM Design: Realising the Creative Potential of Building Information Modeling - John Wiley & Sons, inc, New Jersey, USA KRYGIEL, E., NIES, B. (2008) Green BIM: Successful Sustainable Design with Building Information Modeling - Willey Publishing, Inc, Indianapolis, Indiana, USA KYMMELL, W. (2008) - Building information modeling Planning and Managing Construction Projects with 4D CAD and simulations McGrawHill Nova Iorque USA SMITH, D., TARDIF, M., CSI, H. (2009) Building Information Modeling A strategic implementation guide for architects, Engineers, Constructors, and Real Estate Asset Managers John Wiley & Sons, inc, New Jersey, USA WANG, W., ZMEUREANU, R., RIVARD, H. (2005) Applying multi-objective genetic algorithms in green building design optimization Building and environments - Online References [W1] - Out-law /en/topics/projects- -construction/ projects-and-procurement /building information - modelling/ (December 2015) [W2] - Proton- (December 2015) [W3] CIFE. ( 2007). CIFE Technical Reports - [W4] Earth wall- http: //4.bp.blogspot.com /_EAPvZQFfrh4 /Sy6p4KojX7I /AAAAAAAABRM /9w8zNquNVOY /s400 /getimage.jpg (January 2016) [W5] Stone wall (January 2016) [W6] Wood wall (January 2016) [W7] Brick blcok - (January 2016) [W8] Concrete Block - http: // /FCKeditor /imagens /Image /03.08_- _Cresce_a_constru_o_de_edif_cios_de_alvenaria_com_blocos_de_concreto.jpg(January 2016) [W9] Concrete wall - (January 2016) [W10] LGSF structure - (January 2016) [W11] Prefabricated panels - https: //s-media-cache-ak0.pinimg.com /236x /9e/09 /5b /9e095bc0e c572a5c4037b94c.jpg (January 2016) 10